I have successfully finished the robot. The two read LED and the Green LED are glowing. But there are some questions and problems I need help with.1- When I set the robot for WHITE line follower by following this pic, both motors are on and running.

2- When I set the robot for BLACK line follower as in this pic, both motors stop running.Is this normal or something is wrong with my circuit?

3- Setting the robot for WHITE line follower makes the robot go forward all the time and never makes turns. Am I missing some steps?!!Please tell me what could be wrong with my circuit.

Note: I have attached a pic copied it from the $40 Line Follower site, but realized I could do "insert pic" instead. I tried to find out how to delete the attachment, but couldn't find out how. Sorry for that.

1- When I set the robot for WHITE line follower by following this pic, both motors are on and running.2- When I set the robot for BLACK line follower as in this pic, both motors stop running.Is this normal or something is wrong with my circuit?

3- Setting the robot for WHITE line follower makes the robot go forward all the time and never makes turns. Am I missing some steps?!!Please tell me what could be wrong with my circuit.

Your light sensors are probably way off and you need to change the resistors making up the other part of the voltage dividers.

Measure the voltage at the common node in each pair (LDR and resistor) going to the IC, when the LDR's are "looking" at a piece of white and black paper respectively and report the values here.Pull the IC from its socket while measuring.

I like your project. Your line follower does not use a microcontroller. What it does do is basically compare the inputs from the sensors. (voltage divider) The sensors you have may be the same part as the ones in the tutorial. They may even have been made at the same time but they are not the same. The potentiometers are on the circuit so that you can "balance" the circuit.

You should remove the IC from the socket. Put the sensors over a white piece of paper and then measure the resistance or the sensors where they feed into the chip. Adjust the potentiometers until you can get as close a match as possible. Then your circuit should work much better.

Here is an excerpt from the tutorial you linked. It's from the circuit explanation page.

The resistor whose value is 20K is a potentiometer. A potentiometer (pot or preset) is a resistor whose resistance can be changed. In our project, we will be using 20k presets, that is, we will use presets whose resistance can be changed from 0K to 20K.When the robot is on white surface the light emitted by the LEDs fall on the LDRs and decreases its resistance. This in turn reduces the voltage at Vout. When the robot is on the black line, the light emitted by the LEDs does not reach the LDRs, hence its resistance increases. This in turn increases the voltage at Vout.During both the cases it is necessary to adjust the 20K preset in such a way that, when the robot is on white surface, voltage at Vout is <0.8V (so that the voltage at the emitter of the transistor is LOW) and when the sensor is on the black line the voltage is >0.8V (so that the voltage at the emitter of the transistor is HIGH).

When you turn the trimmers, can you get the LED's to turn on over black and off over white?

I put the sensors over white. No matter which way I turn the trimmers of the presets, the Red LED's are still glowing with no change in the amount of glowing. The Blue LED's do not glow at all no matter how I turn the trimmers.I put the sensors over Black. Same thing as above, No matter which way I turn the trimmers of the presets, the Red LED's are still glowing with no change in the amount of glowing. The Blue LED's do not glow at all no matter how I turn the trimmers.

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Do you have a spare unsoldered LDR so that you can measure its resistance over black and white?

Yes I do. I measured the resistance of unsoldered LDR over black and white. Here are the readings.

LDR over white

LDR over black a bit far from the surface

LDR over black closer to the surface: when exceeding 199.00 the multimeter doesn't show the result.

Have you had any luck getting your project working yet? I just read the tutorial again in much more detail. If your blue LEDs are not glowing I would recommend looking at them to find out why. If I understand the tutorial they are just connected to the robot's battery supply. This circuit is very light dependent. Maybe your don't have enough because the blue LEDs aren't on.

I measured the resistance of unsoldered LDR over black and white. Here are the readings.

Too bad you leave us guessing at what range you measured!

You seem very fond of photos, but in this case, a few written words would tell more than several kB worth of pictures. I'll repeat, Please only use photos when they contribute something!

I'll assume it was on the 200kOhm range(?), so it's around 80k over white and 200kOhm and upwards over black.

As I mentioned, this is where your problem lies.

The LDR's that Pratheek mentions in the parts list comes without specs, but a user has described them as: "Classic CdS (Cadmium-Sulfide) Photoresistors go from very high resistance (about 5 Megohms) in the dark, to very low resistance (about 1 Ohm) in bright sunlight."

Your LDR's are of a higher resistance when in light, so the circuit have to be adapted for this.Either you swap the trimmer potentiometers for some 200k to 500k, or you keep the ones you have and add a resistor to each trimmer where it connects to the +9V line. Break the connection and insert the resistor in between.The trimmer will have much less influence if you just add a resistor, but it will be cheaper and easier.

Start with say a 100k resistor and test if the trimmer can now get it in range.Measure the voltage over the LDR with the trimmer in each outer position and report back your findings...In words please. Only post photos if it explodes, melts or you've got Claudia Schiffer holding your creation.

Logged

Regards,Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?Please remember...Engineering is based on numbers - not adjectives

Sorry about that I thought you might need to see how far my sensors were from the whit and black surface when I measured them.

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I'll assume it was on the 200kOhm range(?), so it's around 80k over white and 200kOhm and upwards over black.

You are correct it was on the 200KOhm.

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keep the ones you have and add a resistor to each trimmer where it connects to the +9V line. Break the connection and insert the resistor in between.

I will take your advice.

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Measure the voltage over the LDR with the trimmer in each outer position and report back your findings...

OK now you may say I am very stupid but here comes the very very beginner's question. How to measure the voltage over the LDR with the trimmer? Do I put the black probe of the multimeter over one lead of an LDR, and the red probe over a track pin of a trimmer?Please be patient with me. I am just a beginner.

Well I am not sure how they are suppose to glow. Do they glow by using light? Can I test them by using a 1.5V battery? I already did but they don't glow either.

This is a picture from the tutorial. The blue LEDs are in the middle and are connected to the red and black lines. Those red and black lines are a power bus. They provide the power to make the LEDs illuminate.

This is a picture from the tutorial. The blue LEDs are in the middle and are connected to the red and black lines. Those red and black lines are a power bus. They provide the power to make the LEDs illuminate.

Ok, I tested 5 new unsoldered blue LED. I used 1k resistor and the 9V battery. They all do not glow. I tested the battery voltage, it's 9.8V.

How to measure the voltage over the LDR with the trimmer? Do I put the black probe of the multimeter over one lead of an LDR, and the red probe over a track pin of a trimmer?

Put the black lead on the pin of the LDR that is connected to ground (0V) and the red lead on the other LDR pin (no problem if you get it reversed, it will just show a minus sign "-" to the left of the voltage reading).

And about your blue LED's...Are they blue or IR LEDs (the latter you won't see with the naked eye)?Did you try swapping their pins, in case you had the polarity wrong?

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Regards,Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?Please remember...Engineering is based on numbers - not adjectives

Your LDR's are of a higher resistance when in light, so the circuit have to be adapted for this.Either you swap the trimmer potentiometers for some 200k to 500k, or you keep the ones you have and add a resistor to each trimmer where it connects to the +9V line. Break the connection and insert the resistor in between.The trimmer will have much less influence if you just add a resistor, but it will be cheaper and easier.

Start with say a 100k resistor and test if the trimmer can now get it in range.Measure the voltage over the LDR with the trimmer in each outer position and report back your findings

I have changed all my trimmer potentiometers to another ones with 250K.I measured the voltage over the LDRs. Here are the readings.right LDRs : 7.38 and 5.84left LDRs : 5.87 and 7.29I measured the voltage of the battery and it was at that time 9.09

After changing all the trimmers to another ones with 250k, the blue LEDs are still not glowing! What is the problem?

Whether or not the blue LEDs glow has nothing to do with the trimmer. If you look at step 4 the red and black wires of the sensor module are soldered to power and ground. That should cause the LEDs to light up. How much voltage do you get between the anode and the cathode of the blue LEDs? A bad connection for the ground wire between the main board and the sensor board my cause the problems you describe.

Maybe we are getting some where now. The Blue LEDs are not affected by the red LEDs or the trimmers. They are connected directly to the battery capacitor. If the blue LEDs have 1.24vdc between their anode and cathode your battery is very low OR you have a problem in your circuit somewhere. The red LEDs are on because the base of the transistors are high. You need enough resistance from the LDR so that the trimmer you put in will drop less then 0.7vdc. When that happens your RED LEDs will go out. The only thing that will cause the red LEDs to extinguish is for the base of the transistor to be low (at less then 0.7vdc.)

The Blue LEDs are not affected by the red LEDs or the trimmers. They are connected directly to the battery capacitor.

OK, I do understand that. But, what function do the blue LEDs do? I thought they suppose to glow only when you put it on the line.Another question, what kind of blue LED should I use for this robot, it's not specified in the tutorial.

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If the blue LEDs have 1.24vdc between their anode and cathode your battery is very low OR you have a problem in your circuit somewhere.

The voltage of the battery at that time was 10.05, it was full charged.I will try to check again for any bad connections in my circuit.

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The red LEDs are on because the base of the transistors are high. You need enough resistance from the LDR so that the trimmer you put in will drop less then 0.7vdc.

Please don't get discouraged with this process. The more problems you have the more you learn.

The blue leds are there to give you consistant results. I mentioned that this circuit was very light dependent. Changes in the lighting in the room could cause the circuit to behave differently from one run to the next. By adding light that is always the same you minimize some of that. That is the function of the blue LEDs.

To get the transistor to go low you need the sensor module to function correctly. The base of the transistor is connected to the center point of a voltage divider. The value of the resistors used in a voltage divider determine what the voltage in the center will be.

www.doctronics.co.uk/voltage.htm. This link was included in the tutorial it should help you understand voltage dividers. That information should help you understand what this circuit should be doing.

If your battery voltage was 10 Vdc and you only got 1.24Vdc at the blue LEDs you HAVE a problem somewhere in your circuit. Look it over carefully. Use a magnifying glass if you have one. Use your multimeter to check for continuity in your circuit both where it should be and where it shouldn't. It's really easy for solder to be somewhere it isn't supposed.

You can use any blue led you want in your circuit. They aren't magic. Just make sure that you don't provide them to much voltage because you can damage them.

Hey...I think I found part of the problem why my four Blue LEDs do not glow.I used four unsoldered blue LEDs to test them. I used a testing board and 1k resistor. Here is what happened.I tested all my four blue LEDs individually with the 1k resistor and 9v battery they all glow. But when I put the four blue LEDs in series with one 1k resistor, they don't glow. Even with only 2 LEDs, they still do not glow.So is the problem with the LED or with the resistor? 1k resistor is what has been suggested in the tutorial.

This is where having a part number for your LEDs is helpful. The datasheet for your LEDs will list their operating voltage. It's possible that after you hook up more then one in series the 1k of resistance that you don't have enough power left to power them. Every item in a series circuit will use some of the available power.

I tested all my four blue LEDs individually with the 1k resistor and 9v battery they all glow. But when I put the four blue LEDs in series with one 1k resistor, they don't glow. Even with only 2 LEDs, they still do not glow.So is the problem with the LED or with the resistor? 1k resistor is what has been suggested in the tutorial.

Each LED needs around 3.6V, so two in series will require 7.2V (plus something to drop over the resistor). More serially connected LED's = Higher voltage needed.A 9V battery goes down to 5.4V before being considered flat and when flat, may still register as close to 9V if measured without a load.Solution: Use the LED's in parallel with a resistor for each (I wonder why they're blue, white LED's would be my choice).

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Regards,Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?Please remember...Engineering is based on numbers - not adjectives